1. Field of the Invention
The present invention relates to a printing unit and a printer.
2. Description of the Related Art
Hitherto, a thermal printer has been known as a printer for printing on a recording sheet (heat-sensitive paper). The thermal printer includes a printing unit that can be reduced in size and weight, and has a simple configuration without using toner or ink. Therefore, the thermal printer is employed for cash registers or mobile terminal devices to be widely used to print various labels, receipts, and tickets.
As the printing unit described above, a so-called “separate-type” printing unit is known. In the separate-type printing unit, for example, a head frame for supporting a thermal head is mounted to a casing main body for receiving a roll sheet therein, whereas a platen frame for supporting a platen roller is mounted to a printer cover that is coupled to the casing main body through an intermediation of a hinge portion so that the printer cover can be operated to be opened and closed.
The above-mentioned separate-type printing unit includes a lock mechanism for maintaining a pressure-contact state between the platen roller and the thermal head when the printer cover is located at a closed position. As the above-mentioned lock mechanism, there is known, for example, a configuration in which engagement concave portions for individually receiving both end portions of the platen roller are formed on the head frame. According to the configuration described above, along with the closing operation of the printer cover, both the end portions of the platen roller are respectively received in the engagement concave portions. At the same time, the thermal head is pressed toward the platen roller by a biasing member to allow the platen roller to be engaged in the engagement concave portions.
On the other hand, in order to disengage the platen roller and the engagement concave portions from each other in the configuration described above, one of the end portions of the platen roller is pushed up by a releasing lever provided to the head frame in a direction of disengaging from the engagement concave portion. At this time, a push-up force exerted on the one end portion of the platen roller is transmitted to the other end portion of the platen roller through the platen frame and the printer cover to disengage both the end portions of the platen roller from the engagement concave portions.
Further, there is known a printing unit comprising a cutter mechanism for cutting a printed recording sheet. The cutter mechanism includes, for example, a movable blade incorporated into the above-mentioned head frame side and a fixed blade incorporated into the above-mentioned platen frame side. According to this configuration, the movable blade is moved in a sliding manner with respect to the fixed blade so as to cut the recording sheet interposed between the movable blade and the fixed blade.
In the configuration described above, however, it is difficult to reliably disengage the platen roller and the engagement concave portions from each other. Specifically, when the push-up force exerted on the one end portion of the platen roller is transmitted to the other end portion of the platen roller through the platen frame and the printer cover, there is a problem in that the printer cover is twisted by the push-up force to cause difficulty in sufficiently transmitting the push-up force to the other end portion of the platen roller. In this case, there is a fear of occurrence of so-called “single-side opening” corresponding to the disengagement of only one end portion of the platen roller from the engagement concave portion. On the other hand, a configuration of reinforcing the printer cover to facilitate the transmission of the push-up force to the other end portion of the platen roller is also conceivable. In this case, however, there is a problem in that the configuration described above disadvantageously leads to rise in manufacturing cost.
Further, as the lock mechanism, for example, there is known a configuration including a pair of lock arms for individually holding both the end portions of the platen roller in concave portions formed on the head frame. According to this configuration, the lock arms are respectively separated away from both the end portions of the platen roller in conjunction with the operation of the releasing lever or the like, thereby enabling the platen roller from being easily disengaged from the concave portions. With the configuration of the lock mechanism described above, however, the lock arms are required to be additionally provided. Therefore, there is a problem in that the configuration disadvantageously leads to increase in number of components and rise in manufacturing costs.
Further, in the cutter mechanism described above, in order to ensure good cutting ability for the recording sheet, a positional relationship between the movable blade and the fixed blade is required to be set so that the fixed blade and the movable blade come into contact with each other at a proper contact pressure when the movable blade slides. To meet such a requirement, there is known, for example, a configuration including a biasing member for biasing the fixed blade so that a cutting edge of the fixed blade is pressed against the movable blade.
In the separate-type printing unit, however, the positional relationship between the movable blade and the fixed blade depends on positional accuracy of the printer cover and the casing main body (such as a position of the hinge portion). For example, an angle of the fixed blade changes depending on the position (height) of the hinge portion with respect to the platen roller. Therefore, when the positional accuracy of the printer cover and the casing main body is low, it is difficult to position the fixed blade and the movable blade with high accuracy when the printer cover is located at the closed position. Thus, there is a fear of lowering the cutting ability.
In view of the matters described above, a printing unit and a printer, which are capable of providing excellent operability while preventing the number of components and manufacturing costs from being increased and positioning the movable blade and the fixed blade with high accuracy to provide excellent cutting ability, are desired in the field of art.